Process of drying mixtures on drying drums



Jan. 11, 1966 G. KETT 3,228,454

PROCESS OF DRYING MIXTURES ON DRYING DRUMS Filed July 23, 1965 A Horn e United States Patent 3,228,454 PROCESS OF DRYING MIXTURES ON DRYING DRUMS George Kett, Norwich, Norfolk, England, asslgnor to Reckitt & Colman (Overseas) Limited, Hull, England, a British company Filed July 23, 1963, Ser. No. 296,953 Claims priority, application Great Britain, July 25, 1962, 28,624/ 62 1 Claim. (Cl. 159-49) This invention relates to an improved method of roller drying of mixtures, for example edible or pharmaceutical mixtures, containing one or more components which, in conventional methods of roller drying, may be adversely affected, for example, they may be subject to discolouration, decomposition or metallic contamination and hence liable to changes and loss of flavour and/or colour during the drying process. The rollers on which the mixtures are dried are usually of steel or cast iron but some of the difiiculties mentioned above occur irrespective of the metal of which the rollers are made. Once dried, the mixtures are removed from the surface of the roller usually by scraping with a doctor blade.

If the mixture to be dried contains one or more acids, then these frequently tend to react with the surface of the roller and thus the dried mix is contaminated with traces of metal compounds. Essential oils are frequently partially decomposed by direct heating and so if they are heated in direct contact with a hot metal surface their degradation products are frequently present in the dried material. This also occurs if the material to be dried contains some edible fat.

The very nature of roller drying causes a large surface area of the mix to be exposed to the atmosphere and if any component of the mix is oxi-dizable, then oxidation may occur.

If the material to be dried contains one or more volatile components then, in the processes of the prior art, there has frequently been loss of these components due to evaporation.

The method according to the invention for producing, by roller drying, a dried mix containing one or more constituents liable to be adversely affected during the roller drying, comprises forming a plurality of separate layers comprising the constituents of the mixture on the roller, allowing the layers to dry on the roller and removing the dried layers as a single film from the roller, and the method is characterised in that the constituents of the layers are chosen so that constituents liable to be affected adversely during the roller drying are shielded from conditions which would cause this to occur by one of the layers.

Generally, in order to obtain uniform distribution, the constituents are applied to the roller in the form of slurries, generally in waters, it is preferred, therefore, that each layer is formed on the roller by applying a slurry of the constituent or constituents of which it is composed and allowing the slurry to dry to form a layer impervious to the next layer being applied.

It is desirable that the first layer should not be completely dry before the next layer is applied to it as, if it is, the heat of the roller transfers very rapidly to the layers being applied, with possible adverse etfects, such as volatile components evaporating rapidly. In other words, the first layers should act as an insulator. If, however, it was not dried appreciably, then it would not be impervious so that the layers would diffuse. For example, a typical slurry being applied may have a water content of about 66% and in this case we find it satisfactory to dry the layer of it to a water content of about 25% before applying the next layer.

The first layer will be of an inert material which substantially does not react with, or in the presence of, the surface of the roller under the conditions at which the process is carried and it is usually applied in the form of a solution or suspension in a carrier medium such as water. Suitable materials include, ground cereals, for example wheat, oat or barley flour. Vegetable tubers may sometimes be used, as they have a high starch content. The choice of the inert material depends largely upon what the other components of the resultant mix are. Apart from acting as a protective layer, this first layer must be, when dried, easily removable from the surface of the roller by, for example, scraping.

If the mix contains a constituent which would deteriorate if in contact with the roller, this constituent my be applied in a second layer. Such constituents may also include, for example, juices, extracts or fine particles of fruit, vegetables, (for example tubers and legumes), meat, fish or cheese, or tea, coffee or cocoa. Other materials, such as sugar, honey, essential oils, or seasonings may be added as desired. This second layer also frequently and advantageously contains an inert material such as that which comprises the first layer.

It the mix contains two or more constituents which would deteriorate if in contact before drying then these constituents are applied in separate layers which are kept apart by a layer to which both constituents are inert.

Among the many dried mixes which may result from the process of this invention may be mentioned fruit juice containing powders, cakes and bread mixes, omelette mixes, vegetable powders as found in purees, for exam le for baby foods, soups, and sauces, and various pharmaceutical powdered mixes, which may then be tabletted or capsulated.

Apparatus for carrying out the process of the inven tion comprises a rotatable roller, which may be of, for example, steel or cast iron, and means for applying two or more separate layers to the roller, means for drying the layers on the roller and means for removing the dried layers from the roller. The means for applying the layers may comprise, for example, sprays, pumps, non-corrodible applicator rollers or combinations of these; alterna tively the roller may pass through a trough containing the material which is to comprise the first layer and then be coated with further layers by either of the previous means mentioned. In a modification of this apparatus twin rollers may be used in which case it is often convenient to feed the material which is to comprise the first layer between the rollers and then to apply the second or succeeding layers by any of the methods mentioned above which are suitable. The separation between the means for applying the separate layers may be adjusted to give the desired degree of drying of one layer before the next is applied.

It is sometimes preferable to incorporate a means for controlling the thickness of one or more of the layers. This may conveniently be done by applying the layers by means of an applicator roller which is adjustable with a micrometer control to control its distance from the roller on which the layer is applied.

The means for drying the layers on the roller preferably comprises means for passing steam through the roller. The means for removing the dried layers from the roller preferably comprises a doctor blade.

The following examples illustrate some aspects of the invention.

Example 1 Steam is passed at a pressure of 50 lbs. p.s.i. through a roller of diameter 18 inches rotating at a speed of 3 r.p.m. A first layer 0.001 inch thick was applied by one applicator roll and a second layer, 0.006 inch thick,

was applied by a. second applicator roll, the two applicator rolls being 6 inches apart. The main roller, is of mild steel Whereas the applicator rolls are, for example, of fescolized or chromium plated mild steel. The slurry from which the first layer is derived is composed of 56% water and 44% wheatfiour and the slurry from which the second layer is derived is composed of 23.8% orange concentrate (73.8% solids), 14.2% honey (82% solids), 44.3% fresh eggs (yolk and white combined) (26.6% solids) and 17.7% Wheat flour. After drying for approximately 18 seconds the resultant dried mix was scraped oil by the doctor blade. Calculated on the dry solids, this mix contained 21.4% comminuted orange, 14.3% honey, 14.3% egg (yolk and white combined) and 50% wheat flour. This is used as a baby cereal.

Example 2 An apparatus similar to that described in Example 1 is used with the modification that three applicator rollers are used, each spaced six inches apart. The first layer, which consists of wheat flour is formed to a thickness of 0.001 inch by applying a wheat flour slurry containing 43% wheat flour and 57% water; the second layer which consists of cocoa is formed to a depth of approximately 0.003 inch by applying a slurry comprising 45% cocoa and 55% water and the third layer, which consists of milk, is formed to a depth of 0.002 inch by applying a milk concentrate comprising 53% milk solids and 47% water. The layers are dried for eighteen seconds and scraped off by a doctor blade. The resultant dried mix, which is used as a baby-milk-cocoa cereal, contained 15% wheat flour, 45 cocoa and 40% whole milk.

Although there has only been described in detail the drying of edible mixtures, any suitable mixture, for example pharmaceutical mixtures, may be dried in similar manner.

Typical apparatus, of the type used in Example 2, is

shown in the accompanying drawing. In this a rotating drying roller 1 is heated by steam entering through pipe 2 and leaving by pipe 3. A layer is applied in contact with the roller by an applicator roll 4, which picks up slurry from a trough 5. A second layer is applied over this layer, after it has dried to some extent, by an applicator roll 6 which picks up slurry from a trough 7. After being dried on the roller 1, the resultant film is removed by a scraper blade 8.

I claim:

A method of producing by roller drying a dried cereal mixture containing at least one constituent from the group consisting of acids and fats which is liable to deterioration by contact with a heated metal roller, which comprises applying a first slurry of ground cereal substantially free of such constituents to a heated roller, drying said first slurry at least partly, and applying to the layer of said first slurry additional slurry containing such constituents to form at least one further layer, said first slurry being dried to a sufficient degree to form a distinct insulating layer indififusable with the additional slurry when such additional slurry is applied, allowing all of the layers to dry on the roller and removing the dried layers as a single film from the roller.

References Cited by the Examiner UNITED STATES PATENTS 866,586 9/1907 Hussey 159-8 X 1,079,673 11/ 1913 Stieller 15911 1,200,116 10/1916 Johnson et al. 15912 X 1,519,561 12/1924 Sucharipa 15811 X 2,119,615 6/1938 Wendeborn 1598 X &92,041 2/ 1940 Headland 99204 2,879,163 3/1959 Anson et a1.

NORMAN YUDKOFF, Primary Examiner. 

